My rig works file with one video card, but once I put a second one in, it seems to not even want to put a display out. It seems like it will boot fine, it just seems to not want to display, which is somewhat important considering I still need to set up the rig.

Did you swap the cards or the monitor cable? With 2 cards, my computer only outputs signal from one of the cards. Have you tried moving the monitor cable from port to port? Again with my computer and DVI, I have to turn off the power before moving the monitor cable. If my computer is one and I move the monitor cable to the right DVI output on the right card, I don't get a signal until I turn the compute off and on.

Maybe there is a switch on your motherboard or a setting in your BIOS to enable/disable SLI (or whatever ATI calls it if it has another name). I know I saw a motherboard with a physical switch to turn on SLI , and perhaps that could potentially make a card that isn't a video card (or a video card without the external linking adapter to the main video card) prevent the main video card from working, thus preventing POST and subsequent boot. I tried to put two video cards in my Fedora 15 box once and it would POST fine (could see video) but once the OS switched to graphics mode, none of the ports had video. In my case (100% different than yours), using the SLI connector didn't help either.

LOL how I could miss that... had a lot of work recently, sorry I was really tried.

It's an nvidia chipset accepting SLI only (NVIDIA). You got an ati, you can't do any crossfire with that motherboard. So it's normal it's not working.

Anyway I re-read everything in your posts and I don't know that PSU, I mean the tradename, never sold those, never bought or even had a flyer about it, maybe there are not targeting canada but the spec seem more than enough so it's good.

For your motherboard... asus make great stuff (currently own Crosshair IV think to go with the V) But the M2N-SLI Deluxe AM2 NVIDIA nForce 570 SLI is reallllly problematic. I don't sell those anymore had to0 much problems. I give an excellent after sell service so it's important for me. I had many issues with that board, RMA 4 of them and the last one was last week, had a problem with ati graphic cards. But with an nvidia, working flawless. That product is kinda banned from my store and my comrades still say "M2N-SLI" to tease me.

My suggestion, change motherboard, take one supporting crossfire.

I can make suggestions and sell one to you if you want, I accept paypal and bitcoins.

I could be mistaken, but I believe SLI and/or Crossfire = Bad for overall hash rate. That said, if SLI can disabled, the fact that the motherboard doesn't support crossfire shouldn't be a problem if not attempting to use it anyway. However, I'm not 100% certain that all boards support multiple video cards anymore. They certainly all did prior to SLI and Crossfire, and the addition of those technologies shouldn't prevent one from using multiple cards independently, but that doesn't mean any given chipset or motherboard manufacturer couldn't screw it up. Regarding ASUS, watch your step with them. I bought a P5WD2 Platinum specifically because they advertised that it supported a SATA multiplier. I bought a multiplier with the matching chipset and it wouldn't work. Support was no help at all and basically ultimately told me that the motherboard didn't support multipliers and engineers were working on it. Because of this, I had to spend several extra hundred dollars to buy a RAID controller to connect everything I had purchased for the build and lucked out in managing to convince the company that sold me the multiplier to take it back.

I could be mistaken, but I believe SLI and/or Crossfire = Bad for overall hash rate. That said, if SLI can disabled, the fact that the motherboard doesn't support crossfire shouldn't be a problem if not attempting to use it anyway. However, I'm not 100% certain that all boards support multiple video cards anymore. They certainly all did prior to SLI and Crossfire, and the addition of those technologies shouldn't prevent one from using multiple cards independently, but that doesn't mean any given chipset or motherboard manufacturer couldn't screw it up. Regarding ASUS, watch your step with them. I bought a P5WD2 Platinum specifically because they advertised that it supported a SATA multiplier. I bought a multiplier with the matching chipset and it wouldn't work. Support was no help at all and basically ultimately told me that the motherboard didn't support multipliers and engineers were working on it. Because of this, I had to spend several extra hundred dollars to buy a RAID controller to connect everything I had purchased for the build and lucked out in managing to convince the company that sold me the multiplier to take it back.

Of course with overclocks, it give me 170 mhs each so 340mhs.Without crossfire GUIminer don't see both cards. But I didn't tried under linux yet. (but other application including windows work well, and multi monitor support)I tried solo card and it's the exact same performance. Of course because both card are close there is more heat but you can resolve that with some great low price case (looking nice too) or with a mcguiver fan.mcguiver fan : http://forum.bitcoin.org/index.php?topic=31383.0;topicseen

Solutions for you

Do more testing, follow those "paranoiac" instructions carefully.

1. Remove any graphic cards, boot, wait 5 real minutes.2. Reset the bios with the jumper. Situed south-east of the board, look in your manual for more details but it's pretty simple.3. Install your card on the second slot ONLY, let the first one empty.4. Boot.5. .6. Profit !

Else :

By now it should work, if not, for an ultimate test, I suggest you to install Windows on a partition or another drive, as you want but make windows 7 running. Install drivers, see what's is going on.

I know linux can be problematic with drivers, for some reason you might have a compatibility problem or he just don't like to have both. Anyway if you can't go in your bios with the second card in the second slot, it's not an OS or driver problem. Try your new card in the first slot only, reset bios, if no result test your card with another board, computer (friends!!) If nothing work, RMA.

Without crossfire GUIminer don't see both cards. But I didn't tried under linux yet. (but other application including windows work well, and multi monitor support)

Sorry to OP for getting further OT, but there are suggestions to try above this post. According to at least one other post I've seen on this forum, having additional cards without SLI/Crossfire in Windows requires a monitor or dummy plug attached to them for the miners to detect them. I ASSUME this means that the monitor/dummy plug has to be set up to clone/extend the desktop. Those same posts all say that's not the same case in Linux (no dummy plug/monitor required), though I can only run cgminer in X on the desktop (they say I could set display=:0 to run it in a remote terminal station), but I don't have to do that step for phoenix/poclbm, so either those miners search the displays or cgminer works different. Regardless, YMMV.